diff --git a/packages/@ant/model-provider/src/shared/__tests__/openaiStreamAdapter.test.ts b/packages/@ant/model-provider/src/shared/__tests__/openaiStreamAdapter.test.ts
index fef15c358..8e8e15000 100644
--- a/packages/@ant/model-provider/src/shared/__tests__/openaiStreamAdapter.test.ts
+++ b/packages/@ant/model-provider/src/shared/__tests__/openaiStreamAdapter.test.ts
@@ -551,7 +551,8 @@ describe('prompt caching support', () => {
 
     const msgStart = events.find(e => e.type === 'message_start') as any
     expect(msgStart.message.usage.cache_read_input_tokens).toBe(800)
-    expect(msgStart.message.usage.input_tokens).toBe(1000)
+    // input_tokens = prompt_tokens - cached_tokens = 1000 - 800 = 200
+    expect(msgStart.message.usage.input_tokens).toBe(200)
   })
 
   test('defaults cache_read_input_tokens to 0 when no cached_tokens', async () => {
@@ -750,7 +751,8 @@ describe('prompt caching support', () => {
 
     // message_delta carries the real values from the trailing chunk
     const msgDelta = events.find(e => e.type === 'message_delta') as any
-    expect(msgDelta.usage.input_tokens).toBe(30011)
+    // input_tokens = prompt_tokens - cached_tokens = 30011 - 19904 = 10107
+    expect(msgDelta.usage.input_tokens).toBe(10107)
     expect(msgDelta.usage.output_tokens).toBe(190)
     expect(msgDelta.usage.cache_read_input_tokens).toBe(19904)
     expect(msgDelta.usage.cache_creation_input_tokens).toBe(0)
@@ -821,7 +823,34 @@ describe('prompt caching support', () => {
 
     const msgDelta = events.find(e => e.type === 'message_delta') as any
     expect(msgDelta.usage.cache_read_input_tokens).toBe(1500)
-    expect(msgDelta.usage.input_tokens).toBe(2000)
+    // input_tokens = prompt_tokens - cached_tokens = 2000 - 1500 = 500
+    expect(msgDelta.usage.input_tokens).toBe(500)
     expect(msgDelta.usage.output_tokens).toBe(100)
   })
+
+  test('subtracts cached_tokens from input_tokens to match Anthropic semantic', async () => {
+    // Anthropic's input_tokens = non-cached tokens only.
+    // OpenAI's prompt_tokens = total input including cached.
+    // The adapter must subtract: input_tokens = prompt_tokens - cached_tokens.
+    const events = await collectEvents([
+      makeChunk({
+        choices: [{ index: 0, delta: { content: 'hi' }, finish_reason: null }],
+      }),
+      makeChunk({
+        choices: [{ index: 0, delta: {}, finish_reason: 'stop' }],
+        usage: {
+          prompt_tokens: 34097,
+          completion_tokens: 30,
+          total_tokens: 34127,
+          prompt_tokens_details: { cached_tokens: 34048 },
+        } as any,
+      }),
+    ])
+
+    const msgDelta = events.find(e => e.type === 'message_delta') as any
+    // input_tokens = 34097 - 34048 = 49 (non-cached input only)
+    expect(msgDelta.usage.input_tokens).toBe(49)
+    expect(msgDelta.usage.cache_read_input_tokens).toBe(34048)
+    expect(msgDelta.usage.output_tokens).toBe(30)
+  })
 })
diff --git a/packages/@ant/model-provider/src/shared/openaiStreamAdapter.ts b/packages/@ant/model-provider/src/shared/openaiStreamAdapter.ts
index 02e32d957..8a14c58db 100644
--- a/packages/@ant/model-provider/src/shared/openaiStreamAdapter.ts
+++ b/packages/@ant/model-provider/src/shared/openaiStreamAdapter.ts
@@ -13,10 +13,10 @@ import { randomUUID } from 'crypto'
  *   finish_reason            → message_delta(stop_reason) + message_stop
  *
  * Usage field mapping (OpenAI → Anthropic):
- *   prompt_tokens                        → input_tokens
- *   completion_tokens                    → output_tokens
- *   prompt_tokens_details.cached_tokens  → cache_read_input_tokens
- *   (no OpenAI equivalent)               → cache_creation_input_tokens (always 0)
+ *   prompt_tokens - cached_tokens             → input_tokens (non-cached input only)
+ *   completion_tokens                         → output_tokens
+ *   prompt_tokens_details.cached_tokens       → cache_read_input_tokens
+ *   (no OpenAI equivalent)                    → cache_creation_input_tokens (always 0)
  *
  *   All four fields are emitted in the post-loop message_delta (not message_start)
  *   so that trailing usage chunks (sent after finish_reason by some
@@ -54,6 +54,9 @@ export async function* adaptOpenAIStreamToAnthropic(
   let textBlockOpen = false
 
   // Track usage — all four Anthropic fields, populated from OpenAI usage fields:
+  // rawInputTokens tracks the raw prompt_tokens (OpenAI total, including cached).
+  // inputTokens is the derived Anthropic value (non-cached only = rawInputTokens - cachedReadTokens).
+  let rawInputTokens = 0
   let inputTokens = 0
   let outputTokens = 0
   let cachedReadTokens = 0
@@ -71,12 +74,17 @@ export async function* adaptOpenAIStreamToAnthropic(
 
     // Extract usage from any chunk that carries it.
     if (chunk.usage) {
-      inputTokens = chunk.usage.prompt_tokens ?? inputTokens
+      rawInputTokens = chunk.usage.prompt_tokens ?? rawInputTokens
+      const rawCached =
+        ((chunk.usage as any).prompt_tokens_details?.cached_tokens as
+          | number
+          | undefined) ?? cachedReadTokens
+      // Anthropic's input_tokens = non-cached input only. OpenAI's prompt_tokens
+      // includes cached tokens, so subtract. Clamp to 0 in case cached > total
+      // due to a streaming race.
+      inputTokens = Math.max(0, rawInputTokens - rawCached)
       outputTokens = chunk.usage.completion_tokens ?? outputTokens
-      const details = (chunk.usage as any).prompt_tokens_details
-      if (details?.cached_tokens != null) {
-        cachedReadTokens = details.cached_tokens
-      }
+      cachedReadTokens = rawCached
     }
 
     // Emit message_start on first chunk